A contract(s) to be awarded in FY 1981 will provide for the development of an aneuploidy test system in the yeast Saccharomyces cerevisiae. It is expected that the contractor(s) will be able to develop a microbial system which will enable the rapid screening of agents that induce aneuploidy meiotic development and mitotic growth. In addition, the system(s) will enable a comparison of the effects of agents in terms of the induction of recombination and mutation as well as aneuploidy. The yeast aneuploid test system will become an integral component in the battery of tests utilized by the Environmental Mutagenesis Test Development Program to detect genetically active agents.